Scientists have shown for the first time that deep-sea fishes that use bio luminescence for communication are diversifying into different species faster than other glowing fishes that use light for camouflage. The new research indicates that bio luminescence, a phenomenon in which animals generate visible light through a chemical reaction could promote communication and mating in the open ocean, an environment with few barriers to reproduction. To investigate, Sparks, Davis, and other scientists from the University of Kansas and Johnson County Community College reconstructed a tree of life for ray-finned fishes with a particular focus on the evolution of bio luminescence.Many fishes emit light from organs called photophores that appear as luminous spots on the body. On lanternfishes, photophores are present ventrally along the belly, laterally on the flank and head, and on the tail. The researchers discovered that the common ancestor of lanternfishes most likely evolved this complex photophore system during the Late Cretaceous, between 73-104 million years ago.Unlike on land, where rivers, mountain ranges, and other physical obstacles can genetically isolate animals from one another resulting in speciation events over time, in the deep open ocean there are few obvious physical barriers to reproduction and gene flow. This has traditionally been considered one of the reasons why there is a comparatively low level of fish species richness in the deep sea. For example, bristlemouths, which are among the most abundant vertebrates on Earth, are represented by only 21 species. But that's not the case for all fishes. Lanternfishes, which inhabit the same mid-water, or mesopelagic, area of the ocean, have diversified into more than 250 species.

What I learned was that the significance of the photophores on the underside of mesopelagic fishes has long been thought to provide camouflage against predators swimming below, helping them to blend in with any light shining down from the surface. The researchers determined that the lateral photophore patterns on certain lanternfish lineages are distinct enough to allow identification of individual species. This is not the case for photophores on the belly. Recent work has shown that lanternfishes are capable of seeing blue-green bioluminescence from up to about 100 feet away, supporting the idea that lateral photophores could be used for interspecific communication. I find this interesting because if I were a fish I could play hide and seek and win easily.

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